I'm about halfway through doing the runs to get those Ki slots on MN/OLB, hard work! Get what you say about Phoenix, it's certainly the worst of the bunch but maxed out it works wonders on the Fiend Dogs and also on Elizabet, you can pretty much kill her outright without ever taking a hit using Phoenix.

The birds are pretty good at stunning fools (and bosses) letting you land more hots. They stay out for a good while. It's more skill based rather than a panic button like the Fire ninpo. As long as you're good at dodging and timing your i-frames you can speed up fights nicely with the Phoenix.